Longitudinal patterns of fish assemblages in European boreal streams

Tapio Sutela,Teppo Vehanen,Pekka Jounela

doi:10.1007/s10750-020-04330-x

Tapio Sutela, Teppo Vehanen + Show 1 more

Open Access

https://doi.org/10.1007/s10750-020-04330-x

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Abstract

Fish assemblages are known to change from headwaters to river outlets. Still, our knowledge of this change is often approximate or sporadic. In this study, we quantified the average longitudinal change from a large electrofishing data set of boreal streams in Northern Europe. The average species richness increased from headwaters to medium-sized rivers but levelled off when reaching large rivers. Existence of some headwater specialist fish species, e.g. brook trout (Salvelinus fontinalis), was interpreted to support the fish zonation concept over the concept of accumulative addition of species downstream. The traditional fish zonation concept developed in Western Europe suggests four zones from headwaters to river outlets, the trout zone, the grayling zone, the barbel zone and the bream zone. Of these, only the trout zone was clearly present with a high dominance in the headwaters of the streams studied. For the North European boreal streams, we suggest a zonation concept with three dominating fish species from headwaters downstream, brown trout (Salmo trutta), bullhead (Cottus gobio) and Atlantic salmon (Salmo salar). Discovered longitudinal shifts in fish guild compositions offered an opportunity for an ecological interpretation of the data and a promising basis for bioassessment.

Highlights

Worldwide, fish assemblages typically differ from the tributaries to lower reaches of streams (Hawkes, 1975; Balon & Stewart, 1983; Matthews, 1986)
Longitudinal changes in the local fish species richness have usually been attributed to biotic zonation or accumulative addition of species downstream (Park et al, 2005)
Brown trout (Salmo trutta) occurred frequently in all stream sizes (Fig. 2), but its average density decreased from headwaters to large rivers (Table 3)

Summary

Introduction

Fish assemblages typically differ from the tributaries to lower reaches of streams (Hawkes, 1975; Balon & Stewart, 1983; Matthews, 1986). Longitudinal changes in the local fish species richness have usually been attributed to biotic zonation (replacement) or accumulative addition of species downstream (Park et al, 2005). Accumulative addition of species from tributaries to lower reaches is usually related to environmental gradients containing smooth transition of abiotic factors (Rahel & Hubert, 1991; Park et al, 2005). The accumulative addition of species downstream and the associated increase in species richness have often been attributed to a downstream increase in habitat diversity (Gorman & Karr, 1978; Schlosser, 1982; Angermeier & Schlosser, 1989) and in environmental stability (Horwitz, 1978; Schlosser, 1982; Park et al, 2005). Smallest streams are often confronted by temporary droughts (Piniewski et al, 2017)

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